A reciprocating saw machine is a hand-held power saw that includes a chuck for releasably engaging the saw blade and driving the saw blade in a reciprocating motion through a work piece. The reciprocating motion can be an orbital cutting action, a straight or linear cutting action, or an angled cutting action. Reciprocating saws are sometimes referred to as recip saws, or jig saws, and reciprocating saw blades likewise are sometimes referred to as recip blades or jig saw blades. Reciprocating saws are typically driven by electric motors (e.g., cord or cordless saws), or are pneumatically driven. Well known reciprocating saws are sold under the brand names “Sawzall™” by Milwaukee Electric Tool Corporation and “Tiger Saw™” by Porter-Cable Corporation.
A typical reciprocating saw blade includes a blade portion having a cutting edge defined by a plurality of teeth axially spaced relative to each other along one side of the blade, and a non-working edge formed on an opposite side of the blade relative to the cutting edge. A tang for releasably connecting the blade to the chuck of a reciprocating saw extends from an inner end of the blade. Typical reciprocating saw blades suffer from the need for a trade-off between maximizing wear resistance and maximizing durability. Harder blade materials tend to be more wear resistant, whereas softer blade materials tend to be more durable. Durability is associated with teeth that are robust, resistant to fracture and/or exhibit an ability to withstand impact.
The teeth of a reciprocating saw blade typically include a cutting tip, a rake face formed on one side of the tip, and a clearance surface extending from the tip and formed on an opposite side of the tip relative to the rake face. The rake face forms a rake angle relative to an axis perpendicular to a reference plane, which may be defined by the plane extending between the tips of successive teeth having substantially the same height, such as successive unset teeth. The clearance surface forms a clearance angle relative to the reference plane.
One way to affect the cutting performance of a reciprocating saw blade is to modify the clearance angle of the cutting teeth. For example, increasing the clearance angle may allow the teeth to cut faster. However, teeth with greater clearance angles may be more delicate and thus more likely subject to breakage than teeth with shallower clearance angles.
The need to restrict the clearance angle is especially acute for reciprocating blades, because the reciprocating cutting pattern is very abusive to blade teeth. In contrast to other types of blades such as band saw blades that continuously move in one direction during cutting, reciprocating blades oscillate back and forth through a work piece in an orbital, linear and/or angular cutting action, and thus create substantial forces on all sides of the teeth.
In addition, because a reciprocating blade must accelerate from zero to maximum speed and back again to zero during each stroke, the blade is at optimal cutting speed during only a portion of the forward stroke, typically less than about 50% of the forward stroke. Furthermore, the length of each stroke is very short, i.e., typically about ¾ inch to about 1¼ inches. As a result, reciprocating saw blades have relatively short repeating tooth patterns of about ½ inch or less to maximize the number of repeat patterns of teeth.
Prior art band saw blades have employed high-low teeth and varying clearance angles. For example, some band saw blades have recurring patterns of groups of teeth wherein each group includes teeth with relatively high tips and teeth with relatively low tips. Band saw blades also have employed teeth with varying clearance angles. Conventional wisdom generally has taught away from applying high-low teeth and/or teeth with relatively steep clearance angles (e.g., about 35° or greater) to reciprocating saw blades. As indicated above, in stark contrast to band saws, for example, reciprocating saws are hand-held power saws that subject the recip blades to an abusive reciprocating cutting action. Thus, not only are the rake faces subject to substantial cutting forces, but the clearance surfaces formed on the back sides of the teeth likewise are subject to substantial cutting forces on the return strokes. Recip blades are particularly susceptible to failure from tooth fracture or chipping. Accordingly, it has been believed that if high-low teeth were applied to a recip blade, the relatively high teeth would be overly exposed and subjected to excessive cutting forces, and thus more likely subject to fracture or chipping. Similarly, it has been believed that if relatively steep clearance angles were applied to recip teeth (e.g., about 35° or greater) any teeth with such narrow included angles would be too delicate to withstand the relatively abusive reciprocating cutting action and associated cutting forces, and therefore would be subject to premature fracture or chipping. Accordingly, the performance of prior art recip blades, such as cutting life and/or durability, have not always been at levels desired.
It is an object of the present invention to overcome one or more of the above-described drawbacks and/or disadvantages of the prior art.